This invention relates to systems for sealing disposable trays that are used for packaging food products and, more particularly, to tray sealing systems which incorporate a beaded seal plate for producing a reliable seal between a sealing film and the tray.
Disposable trays are commonly used for packaging meat and other food products for sale in supermarkets and other retail food outlets. Such trays are typically covered by a clear film to permit the product to be viewed. In one prior art approach, the tray is overwrapped with sealing film by packers in the retail food market. This approach does not provide an airtight seal, and the life of the product is limited. Furthermore, this approach requires additional labor at the retail outlet, and sanitary conditions cannot always be ensured.
Another more recent approach involves case-ready packaging by wholesalers, such as meat packers. A tray sealing system is used to produce an air-tight seal with an inert gas sealed within the package to prevent spoilage. The sealed tray containing a food product is ready for sale when it is delivered to the retail outlet.
The tray sealing systems may include a conveyor for supplying trays containing a food product to a sealing station. The sealing station typically includes a seal support frame for supporting a flange of the tray and a seal plate. The seal support frame is movable between a retracted position and a seal position. In the retracted position, a tray is moved into the seal support frame. In the seal position, the seal plate presses a sealing film into engagement with the flange of the tray. The seal plate is heated, causing the sealing film to be sealed to the flange of the tray.
Experience has shown that contamination of the tray flange is nearly impossible to avoid during packing of the tray with the food product. Such contamination may be liquid, solid, or both and is typically in the form of protein in the case of meat packaging. The contamination makes it difficult to produce an air-tight seal between the sealing film and the tray flange. Even if the tray is sealed initially, the seal may fail prematurely, causing potential leakage and product spoilage.
Accordingly, there is a need for tray sealing systems which overcome the difficulties associated with contamination of the tray flange during the sealing process.
According to a first aspect of the invention, a tray sealing assembly is provided. The tray sealing assembly comprises a seal support frame for supporting a flange of a tray during sealing of a sealing film to the flange, a seal plate having a sealing surface provided with a raised bead, and a heater for heating the seal plate. The seal support frame is movable relative to the seal plate between a retracted position and a seal position in engagement with the seal plate.
Preferably, the raised bead comprises a continuous closed loop on the sealing surface. The raised bead produces a reliable seal between the sealing film and the tray flange, despite the presence of contaminants on the tray flange.
The raised bead may comprise a single closed loop or two or more closed loops on the sealing surface. The raised bead may have a rounded cross section to avoid damage to the sealing film.